The present invention relates to semiconductor wafer processing equipment and, more particularly, to delivery systems for chemical vapors from liquid sources.
In the processing of semiconductor wafers, many processes require the delivery of gases into a processing chamber in which one or more semiconductor wafers are placed. Typically these gases at their sources are in the form of gases, such as nitrogen, oxygen, hydrogen, arsine, etc., in pressurized tanks. However, some processes use gases which are liquid at their sources. The liquid is heated to a vapor which is introduced into the processing chamber.
To create a chemical vapor from liquid sources, delivery systems for liquid sources heretofore have used a bubbler unit or a heated reservoir. In a bubbler unit a inert gas, such as nitrogen, is bubbled through the liquid source to carry the molecules of the chemical along with the inert gas. In heated reservoirs the liquid is heated to vaporize the source chemical for delivery.
In these systems other discrete units, such as valves, pressure and mass flow controllers, and the feedline through which the chemical vapor passes, are connected between the bubbler or reservoir unit and the processing chamber. Each of the discrete units may be heated. In any case, problems arise with these complicated delivery systems. Condensation forms at the unheated or inadequately heated points of the system. Reliability is poor and the consistency of performance is problematical.
Furthermore, the mass flow controllers of these systems have limited performance. These mass flow controllers are difficult to operate at temperatures above 70.degree. C. because they use a heated bypass sensor to sense flow. This sensor has two sections. The first section has (electrical) resistance-heated walls to heat the gas. The second section is unheated and measures the temperature of heated gas from the first section. The difference in temperature of the gas entering the bypass and the gas leaving the bypass is measured to determine the rate of the gas flow. At gas temperatures of 70.degree. C. and above, the difference in temperatures becomes so small that the rate of gas flow is difficult for these present day mass flow controllers to determine. Additionally, the second unheated section is a source of condensation problems.
The present invention solves or substantially mitigates many of these problems of delivering a chemical vapor to a processing chamber from a liquid source. The present invention is integrated and the problems of complexity of present day systems are avoided. Consistency of performance and reliability are greatly improved over present day systems. Furthermore, the present invention is adaptable to even solid sources.